This invention pertains generally to TM.sub.0N0 mode circularly cylindrical cavity power combiners and, in particular, a combiner of such type wherein the TM.sub.020 mode is present and other undesired higher modes are suppressed.
It is known in the art (see U.S. Pat. No. 3,931,587) that a microwave power source may be formed by providing a cylindrical cavity wherein outputs of a plurality of coaxial IMPATT diode oscillators may be combined. In such a source, coaxial IMPATT diode oscillators are symmetrically disposed on the periphery of the cylindrical cavity (which is dimensioned to ensure operation in the TM.sub.010 mode). The number of coaxial IMPATT diode oscillators which may be so disposed is determined by the length of such periphery with the result that the amount of microwave power out of such a combiner is similarly determined.
Obviously, if the length of the periphery of a cylindrical cavity were to be increased a greater number of coaxial IMPATT diode oscillators could be disposed on the periphery of such a cavity with a concomitant increase in microwave power out. However, simply increasing the length of the periphery of a cylindrical cavity, say to support the TM.sub.020 mode, is not feasible because other undesired or higher order modes may also be present. Oscillations in any undesired higher order modes must either be suppressed or be shifted in frequency so that dissipation of power in such oscillations and instability in operation are prevented.